The major objectives of GM13235 are to use the SV40 minichromosome as: 1) A model for exploring the organization, expression and regulation of mammalian genomes. To this end we will study the ability of specific deletion mutants to express various regions of their genome as mature mRNAs. Our aim is to correlate particular segments of SV40's DNA with specific functions in transcription, processing and translation of its genetic information. 2) A vector for tranducing selected genes into cultured mammalian cells thereby permitting more controlled study of their expression and regulation in either episomal or integrated states. All or part of SV40 DNA have been or will be recombined with various bacterial, yeast, viral and mammalian genes to permit their introduction, propagation, integration and expression in established mammalian cell lines. Of particular interest is obtaining vectors with genes whose products provide a selection for cells carrying those genes.